Synthesis and Properties of Isoindoline Nitroxide‐containing Porphyrins

Isoindoline nitroxide‐containing porphyrins were synthesized by the reaction of 5‐phenyldipyrromethane and 5‐(4′‐nitrophenyl)‐dipyrromethane with 5‐formyl‐1,1,3,3‐tetramethylisoindolin‐2‐yloxyl using the Lindsey method. These spin‐labeled porphyrins were further characterized by MS, UV, FTIR, ¹H‐NMR, cyclic voltammetry, electron paramagnetic resonance (EPR), and fluorescence spectroscopy. The electrochemical assay demonstrated that these isoindoline nitroxides‐containing porphyrins had similar electrochemical and redox properties as 5‐carboxy‐1,1,3,3‐tetramethylisoindolin‐2‐yloxyl. Electron paramagnetic resonance test exhibited these porphyrins possessed the hyperfine splittings and characteristic spectra of isoindoline nitroxides, with typical nitroxide g‐values and nitrogen isotropic hyperfine coupling constants. Fluorescence spectroscopy revealed that these porphyrins indicated fluorescence suppression characteristic of nitroxide–fluorophore systems. Moreover, their reduced isoindoline nitroxide‐containing porphyrins eliminated the fluorescence suppression and displayed strong fluorescence. Thus, these isoindoline nitroxide‐containing porphyrins may be considered as the potential fluorescent and EPR probes.